Technical :: Mechanical

By Scott Perry (Simi Valley, California USA)

by Scott Perry (Simi Valley, California)

Posts about the dual carb flow control regulator from the Registry mailing list:


Tim Dapper:

Above is a picture of the mysterious tee fitting (for dual carbed engines). The intent is to sense low fuel pressure, and shut off fuel to the twin carbs. They did not work very well, and were quickly replaced with the electric cut off solenoids. They are notorious leakers. Having one may be authentic, but is not smart.

Larry Edson:

This part is, I believe, only used on the dual carb setup. Its a little round diaphragm about the size of a silver dollar with five nipples coming out of it. Two of them are the in and out for the gas coming from the tank, one is for the outlet from the fuel pump, and the other two go to the carbs. The way I understand it, when it is working it is supposed to prevent backflow from the carbs which I guess in theory could start a fire. I had a Fiat at one time that had incorporated the same concept except they had a second hose going all the way back to the tank. I took the gizmo out of the Fiat, too, to get it to work. Many Type 3s have already had this part replaced with a simple 'T' to cure the problems that a malfunctioning part causes.

There is one other cause that I know of for gas in the oil. As I understand it, if the fuel pump diaphragm has a hole in it gas can get into the engine by that route. The reason you stuff the cavity under the fuel pump with grease is in part to keep gas from leaking down into the engine. When I replace a fuel pump I am always very generous with the grease and I have never had a problem with gas in the oil. Remember, if you can't find a Type 3 fuel pump you have two options. You can get a rebuild kit or you can use a Type 1 fuel pump and unscrew the half dozen screws and rotate the top by one screw hole. That's what I did on my new motor—I just saved the wire bail from the old fuel pump so the Type 3 fuel pump cover would stay on.

Scott Perry:

I remember some time back we had discussions about hard-starting Type 34s after the engine was hot and then shut off for a few minutes. I think I might have a solution...for some anyway. I too have experienced difficulty starting my '65 343 when the engine is hot and I let it sit for anything more than 4 or 5 minutes. When that happens, it almost seems like it's flooded and I have to use all the tricks to get it started which it always does after some cranking.

About two months ago I was down at Bill & Steve's helping Steve out with his computer and when I finally fixed it, he tossed me an NOS fuel valve just for '64-'65 dual-carb Type 3s. He said “we have a few of these we just bought and as I understand it, they keep fuel from going to the carbs after the engine is shut off.” It looks like the “T” fitting I already had in my Type 34 but with a big rounded piece in the center. Anyhow, I took it home and looked it up in the parts book and found out it was part #311 127 405. Sure enough, it's called a “fuel valve” and the application is for dual-carb Type 3s to engine #1 100 000. I also have some Workshop Bulletins from '64 and there was a special bulletin just for this part. As I remember, it listed the part being introduced in mid-late '64 production as a valve to keep fuel from going to the carbs after the engine has stopped. Apparently this was enough of a problem for this part to be introduced. The action of the pump opens the valve when the engine turns so it's purely a simple mechanical piece. In '66 and later Type 3s, they built this valve right into the pump (hence the different pump in '66 on).

Steve said these were produced in response to the dual carbs on pre-'66 Type 3s from filling up and leaking fuel when parked on a hill. Since mine never did that, I didn't bother installing it. To make this long story short, I figured I'd install it for authenticity's sake. It was an easy switch after altering the fuel line lengths just a bit. Now that I've done it, I notice my Type 34 doesn't have the hard starting or flooding problem it had before. Now she starts right up without giving it any gas even after letting it sit for 5, 10 or 15 minutes. This valve must keep the carbs from being flooded. Why they were flooding in the first place is anybody's guess.

I think Bill & Steve's has one or two more so if you're having the battery-draining, starter-wrenching problems I was having, call and pick one up! It an easy fix and authentic for '64-'65 Type 34s.

I checked the Official VW Workshop Manual Bulletins and they list the introduction of this part as August '64 (Update K-98). It says "The twin-carb engines are now being fitted with a fuel line valve (311 127 405) which stops the flow of fuel to the carburetors when the engine is not running. When the engine is started, the pressure from the fuel pump opens the valve." These valves were discontinued with the '66 models since this valve was incorporated into the pump itself. I guess it was a one-year only item that was probably fitted to '64s as they leaked fuel out of the carbs or flooded after the engine was shut off.

The Electromagnetic Cutoff Jet introduction is shown as April of 1964 according to this book. Maybe those cutoff jets weren't doing enough or were intended to accomplish a different task similar to that of the valve

By Jens Vagelpohl, summer 1994 Registry newsletter

By Daniel Baum.